The relative influence of dynamic and static precipitation on the hot ductility of microalloyed steels

TLDR: In this paper, a series of micro-alloyed steels has been obtained after solution treating and cooling to test temperatures in the range 750 to 1000 °C. Various holding times were given prior to testing to vary the amount of prior precipitation from 0 to 100 pct.

Abstract: The hot ductility of a series of micro-alloyed steels has been obtained after solution treating and cooling to test temperatures in the range 750 to 1000 °C. Various holding times were given prior to testing to vary the amount of prior precipitation from 0 to 100 pct. For temperatures corresponding to those giving the maximum rate of precipitation, hot ductility improved with holding time for the Nb containing steels but deteriorated for the V and Al containing steels. It is concluded that dynamic precipitation is most effective in reducing hot ductility for Nb containing steels while static precipitation impairs ductility the most for V containing steels. Whereas precipitation of NbCN and VCN readily occurred, precipitation of A1N was found to be slow and the supersaturation of Al and N had to be high to start the precipitation reaction. There was no evidence for dynamic precipitation of A1N, but static precipitation at γ grain boundaries was effective in reducing hot ductility. Although differences inR of A between samples having no and substantial precipitation prior to deformation were most marked at the temperature corresponding to that giving the maximum rate of precipitation, the temperature range over which significant differences remained could be quite marked.